1. Field of the Invention
The present invention relates to a phase adjustment circuit which adjusts the phase of a sine wave signal with a first phase, a second phase and a third phase in which the phase difference between the respective phases is 120°, a motor driving control circuit which includes this phase adjustment circuit, and which controls the driving of a three-phase brushless motor such as a spindle motor or the like that causes the rotation of an optical disk, and a motor apparatus including this motor driving control circuit.
2. Description of the Related Art
Conventionally, for example, the motor apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-84772 and Japanese Patent Application Laid-Open No. 2003-111481 is known as a motor apparatus of this type. This motor apparatus is shown in FIG. 4. This motor apparatus 101 includes rotational position detection elements HU, HV and HW which are Hall elements that detect the position of the rotor of the motor and output a rotational position signal, a motor driving control circuit 102 which outputs a PWM signal on the basis of the rotational position signal and a command from a motor control command part (not shown in the figures), and a power driver 103 which causes a driving current corresponding to the PWM signal to flow to the armature coils LU, LV and LW of the motor. The rotational position signal is a three-phase sine wave signal consisting of differential U phase signals HU+ and HU− output by the rotational position detection element HU, differential V phase signals HV+ and HV− output by the rotational position detection element HV, and differential W phase signals HW+ and HW− output by the rotational position detection element HW, and the phase difference between the respective phases is 120°.
The motor driving control circuit 102 includes rotational position signal amplifiers 110 through 112 which are three Hall amplifiers that amplify the rotational position signals HU+ and HU−, HV+ and HV−, and HW+ and HW− at a fixed amplification rate, and output sine wave signals U+, U−, V+, V−, W+ and W−, an automatic gain control (AGC) circuit 113 which advances the phase by 30° for each of the sine wave signals U+, U−, V+, V−, W+ and W−, and which amplifies the signals by a gain corresponding to a control voltage that is output by a torque control circuit 118 and outputs signals UHL, VHL and WHL, and three PWM output comparators 114, 115 and 116 which respectively input the signals UHL, VHL and WHL into the non-inversion terminals, input a triangular wave from a triangular wave generator 117 into the inversion terminals (in common), and output PWM signals of the comparison results. Here, the purpose for advancing the phases of the sine wave signals U+, U−, V+, V−, W+ and W− by 30° is to apply a magnetic field with a timing that causes the rotor of the motor to rotate with maximum efficiency. Furthermore, the torque control circuit 118 outputs a control voltage which controls the automatic gain control circuit 113 in accordance with the driving currents of the armature coils LU, LV and LW, and a torque control voltage TORQUE for controlling the motor rotation speed (motor rpm), which is a command from a motor control command part.
However, there is a delay arising from the wiring and the delay (element delay or circuit delay) caused by the operation of the elements and circuits making up the motor apparatus from the time that the rotational position detection elements HU, HV and HW output the rotational position signals HU+, HU−, HV+, HV−, HW+ and HW− until the corresponding driving currents flow to the respective armature coils LU, LV and LW. The phases are shifted as a result of this delay, so that even if the automatic gain control circuit 113 is set at the optimal phase advance angle of 30°, the magnetic field cannot actually be applied to the rotor at the optimal timing.
Generally, the motor rpm of a spindle motor that causes an optical disk to rotate varies according to the read-out speed and write speed of the optical disk. For example, in the case of a CD-R/RW motor apparatus, read-out is performed at a motor rpm of approximately 4,000 to 10,000 rpm, and writing is performed at a motor rpm of approximately 1,000 to 2,000 rpm. Meanwhile, the above-mentioned delay of the motor apparatus is substantially constant regardless of the motor rpm, and the angle corresponding to this delay increases as the motor rpm increases. For example, if the angle is 1.5° at 1,000 rpm, the angle is approximately 9° at 6,000 rpm. Thus, if the motor rpm increases, there is a great shift from the optimal phase advance angle (30°), so that the efficiency of the motor drops. Furthermore, if the shift from the optimal phase angle is large, the waveforms of the rotational position signals HU+, HU−, HV+, HV−, HW+ and HW− are distorted, and the waveforms of the driving currents of the corresponding armature coils LU, LV and LW are also distorted, so that the noise generated by the motor increases.